This invention relates to a method of and apparatus for processing video data signals, to combine a plurality of video data signals into a multiplexed signal.
Video time-division multiplexers (video TDM's) are known in which a plurality of input video data signals, typically from several video cameras, are combined into a single video data stream. This data stream comprises interleaved time-sliced video data or "map shots" from each of the cameras or other video input sources. A typical time-slice or snap shot of a video TDM signal is one field of an input video data signal. Each snap shot or field is typically marked so that the multiplexed video data stream can be separated and reconstructed or decoded into its component parts, which are the original separate input video data signals. The use of video TDM's permits data from a plurality of video sources to be recorded or transmitted on a single medium by time sharing the medium between the different sources, reducing the capital and operating costs of the overall installation.
A disadvantage of known video TDM's is that the time division multiplexed output, by its definition is non-continuous for any one video input source. This is because, for any one video input source, there will be periods of time (during which the remaining of the plurality of the video input sources each have a field inserted into the multiplexed video data signal) that no field or snap shot from that particular video source is inserted into the multiplexed signal. The problem is exacerbated in the case of non-synchronised video sources.
It is an object of the invention to minimise the amount of data which is lost due to this phenomenon.